The present invention relates to rotary magnetic position sensors used to measure angular displacements.
The use of magnetoresistors (MRs) and Hall devices, as position sensors is well known in the art. For example, a magnetically biased differential MR sensor may be used to sense angular position of a rotating toothed wheel, as for example exemplified by U.S. Pat. No. 5,754,042.
Position sensors with digital outputs provide discrete position information only, whereas an analog position sensor can provide both position information and outputs that can be used to drive an electric motor or other similar electromechanical devices. Many of these devices are driven by sinusoidal excitations as a function of position. Consequently, an analog position sensor having an output that varies sinusoidally with position could be used to generate absolute angular positions as, for example, for an electrical power steering system to measure the angle of rotation of the steering wheel, and/or reference signals to produce the desired sinusoidal phase drive currents and voltages to drive electric motors and other similar electromechanical devices.
Accordingly, what remains needed is a compact inexpensive contactless position sensor having a sinusoidally varying output suitable for specialized sensing schemes.
The present invention is a rotary position sensor featuring a magnetized rotor which produces a magnetic flux density that varies sinusoidally with respect to the angular position of the rotor. The magnetic flux density produced by the rotor is measured by a sensor that responds in a linear fashion to the magnitude of the radial component of the magnetic flux density. Typical embodiments would use magnetic flux density sensors, as for example either linear Hall sensors or magnetoresistive type sensors. The measured magnetic flux densities are then used as in a traditional resolver to compute position or used to directly generate control signals to operate, for example, a motor.
Magnetized permanent magnet disks or rings can be used as the rotor to generate signals that vary sinusoidally with respect to position for position determination or for phase current or voltage control for electrical machines, such as motors. Normal position information can be obtained by using two linear magnetic flux density sensors in electrical quadrature. Control of three phase currents or voltages requires a minimum of two sensors spaced 120 electrical degrees apart. The third phase signal being derived from the other two. The use of three sensors spaced 120 electrical degrees apart, in this case, provides a measure of redundancy. Multiple equally spaced sensors could also be used as multiple phase commutation sensors for electric drives requiring multiple phases. Additional sensors may also be included for diagnostic or compensation purposes depending on the application.
According to a first aspect of the present invention, a rotor made of a homogeneous cylindrical permanent magnetic disk or ring is uniformly magnetized in a parallel fashion (i.e. perpendicular to the axis of the cylindrical disk or ring), and produces a sinusoidal radial magnetic flux density in an external constant length nonmagnetic material, such as an air gap. Properly positioned stationary magnetic flux density sensors detect a sinusoidally varying magnetic flux density as the rotor rotates and output a sinusoidally varying signal in response to the sinusoidally varying magnetic flux density.
According to a second aspect of the present invention, a rotor including a continuous cylindrical permanent magnetic ring, or a ring made of discrete magnetic arcuates, is sinusoidally magnetized in a radial fashion (i.e. in a radial direction of a circle perpendicular to the axis of the cylindrical ring or arcuates), and produces a sinusoidal radial magnetic flux density in an external constant length nonmagnetic material, such as an air gap. Properly positioned stationary magnetic flux density sensors detect a sinusoidally varying magnetic flux density as the rotor rotates and output a sinusoidally varying signal in response to the sinusoidally varying magnetic flux density.
According to a third aspect of the present invention, a rotor made of a cylindrical permanent magnetic disk, a continuous magnetic ring or a ring made of discrete magnetic arcuates is sinusoidally magnetized in a tangential fashion (i.e. tangential to a circle perpendicular to the axis of the cylindrical disk or ring), and produces a sinusoidal radial magnetic flux density in an external constant length nonmagnetic material, such as an air gap. Properly positioned stationary magnetic flux density sensors detect a sinusoidally varying magnetic flux density as the rotor rotates and output a sinusoidally varying signal in response to the sinusoidally varying magnetic flux density.
Accordingly, it is an object of the present invention to provide a rotary position sensor according to the first, second, and third aspects of the present invention which is capable of producing and detecting a sinusoidally varying magnetic flux density used to determine angular position of the rotor and/or to provide sinusoidal signals to drive multiple phase electric machines, wherein the rotary position sensor according to the second and third aspects of the present invention are capable of providing sinusoidal signals to drive multiple phase electric machines which require more than two magnetic poles for their operation.
This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment.